The present invention relates to a mobile terminal, a server, and a communication system.
Related-art mobile terminals perform wireless communication with a base station to view or listen to, for example, Web pages or motion picture streams which are distributed from a server connected to the base station. When the mobile terminal is moved to the boundary between the cells and the reception conditions thereof deteriorate, the mobile terminal performs a handover process to be connected to another base station with good reception conditions.
However, a mobile WiMAX terminal conforming to a mobile WiMAX (Worldwide Interoperability for Microwave Access) standard which is one of the mobile communication systems performs a hard handover process to switch base stations connected thereto. In the hard handover process, the mobile terminal is disconnected from the currently connected base station, and then the mobile terminal is connected to another base station. Therefore, communication is temporarily interrupted during the hard handover process. The IP network that has been used before the WiMAX system is generally a wired communication system. In this case, communication is hardly interrupted during a session. In addition, in recent years, a soft handover process has generally been applied to a wireless network anchored by a mobile telephone (3G). In this case, even when the base stations are switched with the movement of the terminal, communication is hardly interrupted. Therefore, the current software based on these network techniques does not perform the flow control of processes (the existing software processes) corresponding to layers higher than the layer that performs the handover process. If the current software based on these network techniques is used without any change, when communication is interrupted, the existing software process is abnormally shut down, which results in an error. Therefore, it is difficult for a mobile terminal (that is, a mobile terminal that performs the hard handover process to switch base stations) conforming to the WiMAX system or a server that distributes content to the mobile terminal to use the existing software without any change, which results in a reduction in convenience.
Patent Document 1 discloses a device for controlling reliable data transmission in a data communication network which includes a mobile terminal. The device has a mobility interface which exists in an IP layer and transmits a notification signal to a layer (for example, a transport layer) higher than the IP layer when the IP layer starts changing a connection point to the data communication network and ends changing the connection point to the data communication network. That is, the device notifies the start and the end of the handover process to the upper layers.
Patent Document 1: JP-A-2005-57397
However, as in the device disclosed in Patent Document 1, the notification of the start and the end of the handover process to the upper layer merely discriminate the interruption of a session in the upper layer due to the network congestion conditions from the interruption of a session due to the connection point handoff conditions of one or more mobile terminals. It is difficult to solve the problem of the process (the existing software process) corresponding to the upper layer being abnormally shut down when communication is interrupted. Therefore, even when the device has a function to notify the start and the end of the handover process to the upper layer, it is difficult to apply the existing software to the mobile terminal that performs a hard handover process to switch base stations or servers that distributes content to the mobile terminal, without any change.